Swimming pool cover

ABSTRACT

A flexible pool cover is stored in rolled condition on a reel at one end of a swimming pool. Cables extend along the pool sides and over a reversing pulley for attachment to a trolley secured to the free cover end. The cable reels and cover reel are driven at the same rotational rate. Means are provided for maintaining the cover and the cables free of substantial slack throughout reeling and unreeling movement.

United States Patent 1 Foster [451 July 24,1973

[ SWIMMING POOL COVER [76] Inventor: Elton Gordon Foster, 147 TrinidadDr., Tiburon, Calif. 94920 [22] Filed: May 12, 1972 [211 Appl. No.:252,580

[52] US. Cl. 4/l72.l4, 160/310 [51] Int. Cl E04h 3/16, E04h 3/18 [58]Field of Search 4/172, 172.14, 172.13,

[56] References Cited UNITED STATES PATENTS 7/1956 Karobonik et al.4/l72.l4 X 8/1959 McGuire ll/l960 Shook et al.. 11/1961 McGuire 4/l72.14

3,019,450 2/1962 Karasiewicz 4/l72.l4 3,050,743 8/1962 Lamb 3,277,49810/1966 Kleinbard et al. 3,426,366 2/1969 Bailey et al.

Primary Examiner-Henry K. Artis Attorney-Colton & Stone [57] ABSTRACT Aflexible pool cover is stored in rolled condition on a reel at one endof a swimming pool. Cables eaitend along the pool sides and over areversing pulley for attachment to a trolley secured to the free coverend. The cable reels and cover reel are driven at the same rotationalrate. Means are provided for maintaining the cover and the cables freeof substantial slack throughout reeling and unreeling movement.

10 Claims, 5 Drawing Figures PATENIEU 3, 747. 132

Sam 2 UF 3 8 mnmmm m HIIIIIIHIIHI FIG. 3

llllll llllllll lllllllllllll I SWIMMING POOL COVER BACKGROUND OF THEINVENTION Swimming pool covers which are advanced and retracted by motoroperated mechanisms are well known in the prior art. One typical typeswimming pool cover involves a spooled cover adjacent one end of thepool, a reversing pulley at the other end of the pool, and suitablecables passed over the reversing pulley and connected at opposite endsto the driving mechanism and the cover. Typical disclosures of this typeare found in U. S. Pat. Nos. 2,754,899; 2,958,083; 3,277,498 and3,426,366. In the typical device of this type, the cable reels and thecover reel are driven simultaneously, either by being mounted on thesame shaft or by connection through single ratio gearing.

There is a substantial problem with simple drives of this type which isa result of the changing diameter of the cover reel'and the cable reels.It will be apparent to those skilled in the art that, at the beginningof cover placement, the cover reel is of larger diameter than the cablereels and the diameter of the cover reel decreases while the diameter ofthe cable reels increases. When beginning the placement of the swimmingpool cover, one revolution of the cover reel pays out a length of coverequal to the circumference of the cover reel while the cable reelsretract a length of cable equal to the circumference of the cable reels.Since the cover reel is of substantially larger diameter than the cablereels, the pool cover becomes slack and tends to wind up on the rollerin the wrong direction when it should in fact be unwinding.

Accordingly, the devices of the prior art present a substantialdisadvantage at the beginning of cover placement. Since the diameters ofthe cover and cable reels approach each other during cover placement,the amount of slack in the cover increases until the diameters of thecover reel and the cable reels are substantially equal. Since the cablereels are increasing in diameter, the amount of slack in the coverdecreases in proportion to the number of revolutions made by the coverand cable reels after their diameters are substantially equal. It willbe apparent that all of the slack may be taken out of the cover and,upon subsequent rotation of the cable and cover reels, the cover isplaced substantially in tension. This also has its disadvantages sincethe cover material may be subject to stretching. It will be apparentthat some care must be exercised in the design of the prior art poolcovers to avoid overtensioning the cover.

It will also be apparent to those skilled in the art that, at thebeginning of cover retraction, the cover reel is of smaller diameterthan the cable reels and the diameter of the cover reel increases whilethe diameter of the cable reels decrease. At the outset of coverretraction, one revolution of the cover reel spools a length of materialequal to the cover reel diameter while one revolution of the cable reelspays out a length of cable equivalent to the circumference of the cablereel. Since the cable reel is of greater diameter than the cover reel atthis point in time, the cable goes slack and tends to wind up on thereel in the wrong direction when it should be unwinding. The cablecontinues to slacken until the diameters of the cable reel and the coverreel are the same at which time the cable begins to tighten.

The prior art has recognized this disadvantage as evi- I denced by U. S.Pat. Nos. 3,019,450 and 3,050,743. In

these disclosures, clutches are provided for the cable reels so that thecable drum is permitted to rotate freely in the unwinding direction asthe cover reel is being driven. Similarly, a one-way clutch is providedfor the cover reel so that the cover reel is permitted to rotate freelyin the unwinding direction as the cable reel is being driven in thewinding direction. While this is a satisfactory technical solution tothe'problem, it will be appreciated that considerable expense isentailed in the provision of the one-way clutches both in initial costand in maintenance.

The device of this invention allows the incorporation of an extremelysimple drive mechanism for the cover and cable reels while maintainingthe cover and cable free of substantial slack.

SUMMARY OF THE INVENTION It is an object of this invention to provide amotorized swimming pool cover including means for maintaining the coverfree of substantial slack throughout spooling and unspooling movementthereof.

Another object of the invention is to provide a mechanized swimming poolcover in which the cover and cable reels are simultaneously driven andincluding resilient means operatively disposed between the drivingmechanism and the cover for allowing differential travel between thecable means and the cover.

In summary, the swimming pool cover of this invention comprises a reelhaving a cover spooled thereon; means operatively connected to the coverfor spooling and unspooling the same across a swimming pool andincluding a reel having thereon spoolable cable means operativelyconnected to the cover and means for simultaneously rotatably drivingthe cover and cable reels; the improvement wherein the spooling andunspooling means includes means for maintaining the cover and the cablemeans free of substantial slack adjacent the respective reel thereofthroughout spooling and unspooling movement, the maintaining meansincluding resilient means in driving connection between the drivingmeans and the cover for allowing differential travel between the cablemeans and the cover.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of oneembodiment of the invention;

FIG. 2 is an enlarged cross sectional view of the trolley which movesalongside the pool during cover placement and retraction and is takenalong line 2-2 of FIG. 1 as viewed in the direction indicated by thearrows;

FIG. 3 is a cross sectonnal view through the cable reels and the coverreel illustrating another embodiment of the invention;

FIG. 4 is a partial plan view of one end of the trolley of anotherembodiment of the invention; and

FIG. 5 is a cross sectional view of the embodiment of FIG. 4, takenalong line 5-5 thereof as viewed in the direction indicated by thearrows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is directedto FIG. 1 wherein there is illustrated a swimming pool 10 containing aquantity of water 12. A motorized swimming pool cover 14 constitutingthis invention is illustrated as substantially covering the pool 10. Theswimming pool cover 14 comprises as major components a sheet or cover16, a roller 18 constituting a reel for the sheet 16, means 20 forunspooling the sheet 16 including cable reels 22, 24 having cable means26, 28 spooled therearound and driving means 30 for driving the roller18 and the cable reels 22, 24.

The sheet or cover 16 may be of any suitable material such aspolyethylene and is wrapped or spooled about the roller 18. As will beapparent from FIG. 1, the sheet 16 is paid out and retracted fromadjacent the top of the roller 18. It is well known that leaves andother debris collect on the sheet 16. Since the sheet 16 is reeled ontothe top of the roller 18, leaves or debris on the sheet 16 pass over thetop of the roll and onto the ground adjacent thereto. The pool owner isthus faced with the rather minor task of cleaning up the pool edgeadjacent the roll 18. If the sheet 16 were taken up along the bottom ofthe roll 18, leaves and debris would be trapped in the spirally woundsheet 16 thereby tending to puncture the same.

The roller 18 may conveniently be a piece of aluminum tubing mounted bysuitable ball bearings or the like (not shown) on a stationary shaft 32mounted on opposite ends thereof by suitable brackets 34. The brackets34 are stationary and may be affixed to the walkway surrounding the poolin any suitable manner.

The unspooling means includes a trolley 36 comprised of an I-beam orother structural member 38 spanning the pool 10. The opposite ends ofthe l-beam 38 are affixed to suitable dollies 40 having wheels 42thereon for traversing the pool 10. The cables 26, 28 are disposed onopposite sides of the pool 10 and extend respectively from the reels 22,24 under suitable idler pulleys 44 through suitable ring guides 46 (FIG.2) and around stationary reversing pulleys 48 for connection to theI-beam 38 in any suitable manner.

The cable reels 22, 24 may be constructed in any suitable manner.Conveniently, the hub of the reels 22, 24 may comprise the roller 18while the reel flanges 50, 52 respectively may comprise annular disksaffixed to the roller 18. In order to drive the roller 18 and reels 22,24, one of the reel flanges 52 may be grooved to receive an endless belt54. l

The driving means 30 includes the endless belt 54 and a driving sheave56 operatively connected to a gear box 58 which is driven by a suitableelectric motor 60 in a conventional manner. The motor 60 is preferably areversing motor controlled by a three-way switch 62. The switch 62allows covering and uncovering of the pool 10 as well as a neutralposition as will be apparent to those skilled in the art.

When the motor 60 is energized to uncover the pool 10, the diameter ofthe cover spool is substantially less than the diameter of the cablereels 22, 24. Accordingly, the cables 26, 28 pay off cable more rapidlythan the sheet 16 is wound onto the roller 18. The cables 26, 28accordingly tend to wind in the wrong direction about the reels 22, 24rather than unwind. Basically, the same problem occurs with the sheet 16when it is in the process of being placed over the pool 10.

To overcome this disadvantage and still provide an extremely simpledrive mechanism for the roller 18 and reels 22, 24, the cables 26, 28are, in accordance with one embodiment of this invention, selected froma known group of resilient tensile force transmitting means. This groupis known in the boating arts as shock cord and is normally used insteadof rope to fasten boat fixtures where some elasticity is desired orrequired. Shock cord is commercially available through most boatingsupply stores and is commonly constructed of elastic rubber strands witha woven sleeve or overlay of nylon. One manufacturer of shock cord is N.A. Taylor, Inc., of Waxahachie, Texas. The diameter of the shock cordmay vary widely depending on the length of the pool, the elasticityrequired, and the weight of the sheet 16. As might be expected, thediameter of a typical shock cord decreases significantly du ringstretching. A typical shock cord elongates approximately 30 per centwhen placed under about 100 pounds tension. Substantial elasticity isrequired in the normal pool installation since the differential travelof the cables 26, 28 with respect to the sheet 16 is in the range of l-8feet and typically is about 6 feet.

By utilizing a typical shock cord for the cables 26, 28, there issufficient elasticity in the cable means to allow spooling andunspooling of the sheet 16 without creating substantial slack in eitherthe cables 26, 28 or the sheet 16. Accordingly, the practice of thisinvention allows an extremely simple drive arrangement wherein the cablereels 22, 24 and the roll 18 are driven simultaneously and yet avoidsthe creation of substantial slack in either the sheet 16 or the cables26, 28.

Referring to FIG. 3, there is illustrated another embodiment of theinvention. FIG. 3 comprises a longitudinal cross sectional view throughthe cover roll and the cable reels as will be more fully apparenthereinafter. FIG. 3 illustrates a motorized swimmlng pool cover 64having a sheet or cover 66 spirally wound about a roller 68. The roller68 is mounted by suitable ball bearings 70 for rotation about astationary shaft 72 which is supported at opposite ends thereof bysuitable brackets (not shown). Axial movement of the roll 68 isprecluded by suitable thrust plates 74 which are affixed to thestationary shaft 72 in any suitable manner.

Comprising a part of a driving means similar to that illustrated in FIG.1 is a sheave 76 which is affixed to the roller 68 in any suitablefashion. As is illustrated in FIG. 3, the sheave 76 not only acts todrive the roller 68 but also bears against the thrust plate 74. It willaccordingly be seen that the roller 68 is directly driven by the sheave76 in a 1:1 ratio.

There is also provided a pair of cable reels 78, 80 which are drivensimultaneously with the roller 68 but which do not necessarily rotate atthe same velocity. The reels 78, 80 are generally S-shaped in crosssection and comprise radiating plates 82, 84, 86 and 88, 90, 92respectively. l-lubs 94, 96 define, with the walls 84, 86 and 88,respectively, a pair of cable receiving areas as in a conventional reel.Circumferential'plates 98, 100 define, with the walls 82, 84 and 90, 92respectively, a pair of spring housings incorporated in the reels 78,80. The reels 78, 80 are mounted for rotation about the roller 68 byhousing and spool bearings 102, 104, 106, 108. Suitable thrust collars110, 112 are affixed to the roller 68 and prevent inward movement of thereels 78, 80 respectively. Outward movement of the reel 78 is precludedby a thrust collar 114 acting between the thrust plate 74 and thehousing bearing 102. Outward movement of the reel 80 is prevented by thehousing bearing 106 abutting the sheave 76.

Disposed in the spring housing of each of the reels 78, 80 is a spirallywound spring 116, 118 having one end thereof affixed to the roll 68 andthe other end thereof affixed to the circumferential plate 98, 1011respectively.

Suitable cables 120, 122 are operatively connected to the reels 78, 80and are connected to a suitable trolley as in the embodiment of FIG. 1for spooling and unspooling the cover 66 across a swimming pool. It willbe apparent'that the elasticity afforded by the springs 116, 118operates in much the same manner as the resilient cable means 26, 28 ofFIG. 1 to prevent excessive slack developing in the cover 66 and thecables 128, 122 during covering and uncovering of the swimming pool.

As is apparent from the relative amount of spooled cable 120, 122 andspooled cover 66, FIG. 3 illustrates the situation where the cover 66 isplaced over the swimming pool. When the sheave '76 is driven in thecover spooling direction, the length of the cable 120, 122 paid out isgreater than the length of cover 66 spooled onto the roller 68. Thus,the cable 120, 122 becomes slack and tends to wind up in the wrongdirection. The springs 116, 188 accordingly elongate and retard rotationof the reels 78, .80 and retard payout of the cable 128, 122 to maintainthe same reasonably taut. Continued spooling of the cover 66 createsaddi- 6 out of cable 120, 122.

Referring now to FIGS. 4 and 5, there is illustrated another embodimentof the invention. FIGS. 4 and 5 illustrate a trolley 124 comprising anl-beam or other structural member 126 spanning a swimming pool. Thetrolley 124 includes a dolly 128 on each side thereof having wheels 1311enabling the trolley 124 to traverse the length of the pool. Affixed'tothe web of the I-beam 126 is a mounting plate 132 carrying a stationarystub shaft 134. A thrust plate 136 is affixed to the end of the stubshaft 134 and captivates thereon a take-up reel 138. The take-up reel issubstantially identical to the reels 78, 80 and includes a cablereceiving area 140 and a spring housing 142 mounted together forrotation about the stub shaft 134 by bearings 144', 146. A spiral spring148 is positioned in the spring housing 142 and has one end affixed tothe stub shaft 134 and the other end affixed to the cable housing 142. Acable 150 is spooled onto a driving reel of the type shown in FIG. 1 andpasses around a reversing pulley, also as shown in FIG. 1, and is thenattached to the take-up reel 138. The tension in the cable 150 iscontrolled by how tightly the spring 1481s wound.

To provide a comparison of the embodiments of this tional slack in thecables 120, 122, which is accommoinvention, the following table isprovided:

Embodiment of- Relation of cover Result without When speed to cablespeed this invention FIG. 1 FIG. 3 FIGS. 4 plus 5 Start of cover payCover pay out rela- Cover to slack Cables 26, 28 shorten to Springs 116,118 elongate Spring 148 elongates to out. tlvely too fast. move trolleyrelatively to take up cable and Mid-point of cover Cover pay out rela-Coyer begins to faster. Cables 26, 28 elongate take up cable and movetrolley faster. Spring 148 compresses move trolley faster. Springs 116,118 compress pay out. tively too slow. tighten. to move trolley slower.to pay out additional to pay out additional cable and move trolley cableand move trolley slower. slower. Start of cover Cable pay out rela-Cable too slack Cables 26, 28 shorten to Springs 116, 118 elongateSpring 148 elongates to retraction. tively too fast. inotve trolleyrelatively to take up cable. to take up cable.

as er. Mid-point of cover Cable pay out rela- Cable begins to Cables 26,28 elongate to Springs 116, 118 compress Spring 148 compressesretraction. tively too slow. tighten. move trolley slower. to bplay outadditional to bplay out additional ea c. ea e. End of cover retraction.

dated by further elongation of the springs 116, 118. As the diameter ofthe spooled cover 66 passes that of the reeled cable 120, 122, thelength of the cover 66 spooled per revolution is greater than the lengthof cable 120, 122 paid out from the reels 78, 88. The cables 128, 122accordingly begin to tighten and thereby compress the springs 116, 118to pay out additional length of the cable 128, 122.

At the start of cover pay out, the diameter of the spooled cover 66exceeds that of the reeled cable 120, 122 causing excessively rapidcover pay out. As a result, the cover 66 becomes slack. The springs 116,118 begin to expand thereby taking up additional lengths of 'cable tomove the trolley (not shown) an additional incremental length andthereby take the slack out of the cover 66. Until the diameter of thespooled cover 66 equals the diameter of thereeled cable, cover pay outis relatively too fast tending to induce slack in the cover. The springs116, 118 continue to expand thereby taking up additional or incrementalcable lengths to move the trolley slightly faster and take the slack outof the cover 66. As the cover 66 approaches the'end of its unspoolingtravel, the diameter of the spooled cover is less than the diameter ofthe reeled cable such that cover pay out is relatively too slow. Sincecover pay out is relatively too slow, the tension in the cables 120,1122 increases thereby compressing the springs 116, 118 effectivelyallowing additional pay The inspection of the foregoing summary willillustrate that the resilient components of the various embodiments ofthis invention undergo a cyclical lenthening and shortening. It shouldbe apparent that, for example at the start of cover pay out with theembodiment of FIG. 1, the cables 26, 28 should be stretched to allowshortening during the initial portion of cover pay out. Similarly, thesprings 116, 118 of the embodiment of FIG. 3 should be compressed to asignificant extent in order to take up cable during the initial portionof cover pay out.

Another important feature of the invention resides in the provision of aplurality of attachments 152 (FIG. 1) and 154 (FIG. 4) between thel-beams 38, 126 and the respective covers. Using FIG. 1 as exemplary,the attachments 152 comprise the force transmitting connection betweenthe l-beam 38 and the cover 16. When the l-beam 38 is moving away fromthe roller 18, the attachments 152 are in tension to pull the cover 16off the roller 18. When the I-beam 38 is moving toward the roller 18,the attachments 152 are in tension and the sheet 16 is pulling thetrolley 36.

One substantial difficulty with swimming pool covers occurs after asubstantial rainfall. Since the cover 16 is desirably impermeable,rainfall accumulates thereon. Using a 20 feet X 40 feet swimming pool asexemplary, a 2 inch rainfall accumulation weighs approximately 8,300pounds. Initial retraction of the cover 16 is not a substantial problemsince the cover 16 slides through the water. A substantial problemexists at the termination of cover retraction. Since the trolley 36 andthe roller 18 are above the water level, the cover 16 assumes anupwardly concave configuration when the trolley 36 approaches the roller18. Under this circumstance, the cover 16 would have to be verticallylifted to completely retract the same. Even if only 10 percent of theaccumulated rainfall remains on the cover 16, the weight to be lifted bythe roller 18 is so substantial as to prevent complete retraction of thecover 16.

To overcome this difficulty, the attachments 152 are selected of apredetermined length of flexible materials. The minimum length of thestretched attachments 152 is the distance from the I-beam 38 where theattachments 152 are secured and the water 12, so that the cover 16 doesnot assume an upwardly concave configuration when loaded with rainwater.The maximum length of the unstretched attachments 152 is the distancefrom the l-beam 38 where the attachments 152 are secured to a pointabove the water 12 to avoid dipping the leading edge of the cover 16into the water when the cover 16 is not loaded with rainwater. In thetypical pool installation, this length of the unstretched attachments152 is between 4-l0 inches. In a prototype constructed in accordancewith the invention, the optimum length of the unstretchable attachments152 proved to be 5 inches.

Although the attachments 152 may be made of any flexible materialmeeting the above criteria, they conveniently are the same material asthe cables 26, 28.

I claim:

1. A swimming pool cover of the type comprising a reel having a coverspooled thereon; means operatively connected to the cover for spoolingand unspooling the same across a swimming pool and including a reelhaving thereon spoolable cable means operatively connected to the coverand means for simultaneously rotatably driving the cover and cablereels; the improvement wherein the spooling and unspooling meansincludes means for maintaining the cover and the cable means free ofsubstantial slack adjacent the respective reel thereof throughoutspooling and unspooling movement, the maintaining means includingresilient means in driving connection between the driving means and thecover for allowing differential travel between the cable means and thecover.

2. The swimming pool cover of claim 1 wherein the resilient meanscomprises the cable means.

3. The swimming pool cover of claim 1 wherein the resilient meansconsists essentially of the cable means.

4. The swimming pool cover of claim 1 wherein the differential travelbetween the cable means and the cover lies in the range of 1-8 feet.

5. The swimming pool cover of claim 1 wherein the resilient meanscomprises cable takeup means.

6. The swimming pool cover of claim 5 wherein the cable takeup meanscomprises a resiliently biased takeup reel between the cable means andthe cover.

7. The swimming pool cover of claim 1 wherein the resilient meanscomprises means allowing differential rotation of the cable reel and thecover reel.

8. The swimming pool cover of claim 7 comprising means mounting thecable reel for free rotation about an axis and the resilient meanscomprises a spring drivably interconnecting the driving means and thecable reel.

9. The swimming pool cover of claim 8 wherein the spring comprises aspiral spring.

10. A swimming pool cover of the type comprising a reel having animpermeable cover spooled thereon; means operatively connected to thecover for spooling and unspooling the same across a swimming pool andincluding a trolley for traversing the pool, means for moving thetrolley and attachment means connecting the trolley to the cover; thecover defining a path of movement along the surface of water in theswimming pool and then upwardly adjacent the edge of the pool, thetrolley being above the water surface; the improvement comprising meansfor removing accumulated rainwater from the top of the cover at thecompletion of spooling movement of the cover, the removing meansincluding the attachment means, the attachment means comprising flexibleelements having a minimum stretched length sufficient to reach the watersurface and a maximum unstretched length insufficient to reach the watersurface.

i i t i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent3.747.132 Dated Julv 24, 1973 lnvent fl Elton Gordon Foster It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Change patentee's address from 147 Trinidad Drive, Tiburon, California94920 to 2034 Dryden Road, Houston, Texas 77025. 7

Signed and sealed this 30th day of April 197R.

(SEAL) Attest:

EDWARD I-I.FLETCHER,JR. C. MARSHALL DANN Atte sting Officer Commissionerof Patents I FORM 90-1050 (10- uscoMM-oc 60376-P69 h US GOVERNMENTPRINTING OFFICE I969 O-366-3 4

1. A swimming pool cover of the type comprising a reel having a coverspooled thereon; means operatively connected to the cover for spoolingand unspooling the same across a swimming pool and including a reelhaving thereon spoolable cable means operatively connected to the coverand means for simultaneously rotatably driving the cover and cablereels; the improvement wherein the spooling and unspooling meansincludes means for maintaining the cover and the cable means free ofsubstantial slack adjacent the respective reel thereof throughoutspooling and unspooling movement, the maintaining means includingresilient means in driving connection between the driving means and thecover for allowing differential travel between the cable means and thecover.
 2. The swimming pool cover of claim 1 wherein the resilient meanscomprises the cable means.
 3. The swimming pool cover of claim 1 whereinthe resilient means consists essentially of the cable means.
 4. Theswimming pool cover of claim 1 wherein the differential travel betweenthe cable means and the cover lies in the range of 1-8 feet.
 5. Theswimming pool cover of claim 1 wherein the resilient means comprisescable takeup means.
 6. The swimming pool cover of claim 5 wherein thecable takeup means comprises a resiliently biased takeup reel betweenthe cable means and the cover.
 7. The swimming pool cover of claim 1wherein the resilient means comprises means allowing differentialrotation of the cable reel and the cover reel.
 8. The swimming poolcover of claim 7 comprising means mounting the cable reel for freerotation about an axis and the resilient means comprises a springdrivably interconnecting the driving means and the cable reel.
 9. Theswimming pool cover of claim 8 wherein the spring comprises a spiralspring.
 10. A swimming pool cover of the type comprising a reel havingan impermeable cover spooled thereon; means operatively connected to thecover for spooling and unspooling the same across a swimming pool andincluding a trolley for traversing the pool, means for moving thetrolley and attachment means connecting the trolley to the cover; thecover defining a path of movement along the surface of water in theswimming pool and then upwardly adjacent the edge of the pool, thetrolley being above the water surface; the improvement comprising meansfor removing accumulated rainwater from the top of the cover at thecompletion of spooling movement of the cover, the removing meansincluding the attachment means, the attachment means comprising flexibleelements having a minimum stretched length sufficient to reach the watersurface and a maximum unstretched length insufficient to reach the watersurface.